Composition and method for treatment of lead-containing surface coatings and soil

ABSTRACT

A method is provided to render non-hazardous surface soil which is contaminated with lead compounds. The soil is treated by applying an aqueous composition comprising hydrogen peroxide, ammonium hydroxide, nitric acid and acetic acid and allowing said composition to migrate through the soil.

This application is a division of Ser. No. 08/599,632 filed Feb. 9, 1996now U.S. Pat. No. 5,741,366.

BACKGROUND OF THE INVENTION

The present invention relates to compositions for the treatment oflead-based and lead-containing surface coatings or soil for the purposeof rendering said surface coatings or soil non-hazardous to humans.Specifically, the compositions are useful for the removal of lead-basedpaints from interior and exterior surfaces of a structure and for thetreatment of lead-contaminated soil.

Lead-based coatings, for example, lead-based paint, may contain suchcompounds as lead chromate, lead molybdate, lead sulfate, lead borate,lead carbonate, lead monoxide, lead tetroxide, lead vanadate and leadantimonate. Soil surrounding public, private or Indian housing andstructures of business may contain tetraethyl lead and perhaps otherlead compounds.

Title X--Residential Lead-based Paint Hazard Reduction Act of 1992defines by amendment to the Toxic Substances Control Act "lead-basedpaint" as paint on surfaces with lead in excess of 1.0 mg/cm² asmeasured by a spectrum analyzer or direct reading x-ray fluorescence(XRF) detector, or 0.5 percent by weight. The XRF threshold had beenestablished in the 1988 amendment to the Lead-based Paint PoisonPrevention Act and remains unchanged. Title X's explicit standard of 0.5percent by weight focuses attention and resources on surfaces with highlevels of lead.

Title X also defines "lead-based paint hazard" as any condition thatcauses exposure to lead sufficient to cause adverse human health effectsand it cites six situations which are:

Deteriorated lead-based paint such as any exterior or interiorlead-based paint that is peeling, chipping, chalking or cracking, or islocated on any surface or fixture that is damaged or deteriorated.

Lead-based paint on any "friction surface", an interior or exteriorsurface subject to abrasion or friction, such as painted floors.

Lead-based paint on any "impact surface", an interior or exteriorsurface subject to damage by repeated impacts such as parts of doorframes.

Lead-based paint on any "accessible surface", an interior or exteriorsurface accessible to a young child to mouth or chew, such as a windowsill.

"Lead-contaminated dust", surface dust in residential dwellings thatcontain an area or mass concentration of lead in excess of the standardto be established by the Environmental Protection Agency.

"Lead-contaminated soil", bare soil on residential property thatcontains lead in excess of the standard to be established by theEnvironmental Protection Agency.

Title X also defines "abatement" as any set of measures designed topermanently eliminate lead-based paint hazards in accordance withstandards established by appropriate Federal agencies. Such abatementincludes:

(A) the removal of lead-based paint and lead-contaminated dust, thepermanent containment or encapsulation of lead-based paint, thereplacement of lead-painted surfaces or fixture and the removal orcovering of lead-contaminated soil; and

(B) all preparation, clean-up, disposal and postabatement clearancetesting activities associated with such measures.

Present state-of-the-art procedures for removing lead-based paint haveserious disadvantages. The procedure described in U.S. Pat. No.4,426,250 uses very caustic chemicals such as hydroxides of sodium,potassium, calcium and magnesium. A paste containing such chemicals isapplied to the painted surface and is then covered with a fabric duringat least part of the treatment period. The method is time consuming andrelatively hazardous.

In recent years, the most commonly used paint stripping compositionshave contained halogenated hydrocarbon chemicals, such as methylenechloride. Since such chemicals are suspected to be carcinogenic, therehave been many attempts to replace them with combinations of otherorganic chemicals. U.S. Pat. No. 5,089,164 is one reference whichdescribes paint stripping compositions which contain among other organicconstituents a significant amount of N-methyl-pyrrolidone. It is ourunderstanding that in the presence of water these compositions havesignificantly lower stripping rates than compositions containingmethylene chloride and that organic stripping agents are not easilywashed from the stripped surface.

Some stripping compositions have contained peroxides such as thosedescribed in U.S. Pat. No. 3,355,385. These compositions, however,contain very volatile and flammable solvents which render the life ofthe composition as a stripping agent very short. U.S. Pat. No. 5,215,675combines the use of hydrogen peroxide with water soluble esters inaqueous stripping compositions to eliminate such problems.

All of the above stripping compositions contain organic solvents andstripping agents which are not easily washed from the treated surface.Also, none of these references indicate that the compositions are usefulfor the stripping of lead-based paints.

Treatment of lead in soil has been limited in the prior art toimmobilizing the lead by converting lead containing compounds tonon-leachable forms. Examples of such immobilization are shown in U.S.Pat. Nos. 5,162,600, 5,202,033 and 5,234,485.

It is an object of this invention to provide an effective aqueous basedcomposition for the abatement of lead whether it be in lead-based paintor in surface soils.

SUMMARY OF THE INVENTION

This invention provides an improved chemical composition which isformulated to render non-hazardous all surfaces which have been coatedwith lead-based paints and surface soil which is contaminated with leadcompounds. The chemical composition is an aqueous mixture comprisingabout 10 to 20 percent by volume of a 30% by weight hydrogen peroxidesolution, about 10 to 20 percent by volume ammonium hydroxide, about 10to 20 percent by volume concentrated nitric acid, about 10 to 20 percentby volume glacial acetic acid, the remainder being water.

DETAILED DESCRIPTION OF THE INVENTION

When mixed in the approximate amounts of the following parts by volume;namely, one part of a 30% by weight hydrogen peroxide solution, one partammonium hydroxide, one part concentrated nitric acid, one part glacialacetic acid and three parts distilled water; a solution is formed whichcan be advantageously used to render non-hazardous all surfaces whichare coated with lead-based paints of any composition and surface soilswhich are contaminated with lead in any form. When treated with asolution containing all four of the above mentioned components, alllead-based paints and coatings are decomposed and can be easily removedfrom the surface on to which they have been coated.

When the solution is to be used on a vertical or near-vertical surface,it may be desirable to add to the mixture one or more thickening agentssuch as gelatin, flour, starches, cellulose compounds, and clays. Byraising the viscosity of the solution it may adhere to a given surfacefor a longer period of tome and allow a more effective use of thecomposition. Such thickening agents do not affect the performance of thesolution in rendering surfaces non-hazardous.

The solution when constituted with all four of the above mentionedingredients will also substantially remove all types of lead compoundsfrom surface soil when the solution is passed through the soil. Currentstandards are that an area on a residential property on which the soilcontains more than 0.50% by weight lead must be paved over or the soilremoved. In soil immediate to house perimeters the upper acceptablelimit is 0.20% by weight lead. In children's play areas and alike theupper acceptable limit is 0.04% by weight lead. One can see from thefollowing examples that the compositions of this invention can beeffective in reducing the lead content of soil to acceptable limits.

The following examples are given to show the invention and its use. Theyare not meant to be restrictive in any way.

EXAMPLE 1

A fuel oil storage tank was found to have a coating which contained 0.6mg/cm² of lead determined by a surface measurement performed using aspectrum analyzer X-ray fluorescence (XRF) detector. 70 cc of a mixtureof three parts distilled water, one part 30% hydrogen peroxide, one partammonium hydroxide, one part concentrated nitric acid and one partglacial acetic acid (all by volume) was poured on the vertical side ofthe coated tank. It ran down the side of the coated tank reacting withthe surface which it contacted and removing the paint from the surfacewhich it contacted. Distilled water was poured onto the same surface toneutralize it and the surface was dried with a cloth. The treatedsurface was found to be non-hazardous by testing with NIOSH method 0700(Lead in Surface Wipe Samples). The analysis of the wipe sample was lessthan 10 μmg/ft².

EXAMPLE 2

A window sill whose surface contained 9.8 mg/cm² of lead as measured byan XRF spectrum analyzer was treated with a solution with the samecomposition as described in Example 1. After being poured on the surfaceof the window sill, there was a reaction of the solution with the painton the surface as indicated by bubbling and foaming of the solution.Reaction had subsided after about two hours at which time distilledwater was poured on the surface to neutralize the material on thesurface and the surface was wiped dry. After drying, the lead content ofwhatever remained on the surface was found to be in corners, where caulkhad been used on top of the paint, to be 0.79 mg/cm² and on the flatsurfaces to be 0 mg/cm². The surface residual material was shown to benon-hazardous by the NIOSH method 0700 which showed a wipe analysis ofabout 200 μgm/ft².

EXAMPLE 3

A sample of surface soil was found to contain 0.52% by weight lead usinginductively coupled plasma atomic emission spectroscopy. 0.12 ft³ ofthis soil was placed in a colander and 70 cc of a solution made asdescribed in Example 1 was distributed evenly over the surface of thesoil. Over a twenty-four hour period some of the liquid passed throughthe soil and was evaporated. The treated soil was then found to containonly 0.22% by weight lead as measured by inductively coupled plasmaatomic emission spectroscopy.

EXAMPLE 4

A second sample of surface soil containing 0.52% by weight lead asmeasured by inductively coupled plasma atomic emission spectroscopy wastreated in exactly the same manner as the sample in Example 3. Thetreated soil was found to contain 0.14% by weight lead as measured bythe same means.

EXAMPLE 5

A sample of surface soil was found to contain 1.00% by weight lead ayinductively coupled plasma atomic emission spectroscopy. 0.12 ft³ of thesoil was treated as described in Example 3. After treatment the soilcontained 0.18% by weight lead as measured by the same means.

EXAMPLE 6

A deteriorated lead-based painted surface showed 9.8 mg/cm² using thespectrum analyzer XRF detector. 10 grams of paint chipped from thissurface were treated in a glass jar with 140 cc of solution thecomposition of which was the same as the solution described inExample 1. After 24 hours the solution was poured from the chips andthey were rinsed with about 200 cc of distilled water. At this point thechips contained 0.08% by weight lead as determined by inductivelycoupled plasma atomic emission spectroscopy. This is much below the 0.5%level considered to be hazardous.

EXAMPLE 7

A representative sample of surface soil contaminated with lead and thesoil beneath it was placed in a clear plastic cylinder which was 137 cmlong and had an internal diameter of 11.4 cm. The bottom 122 cmcontained uncontaminated subsurface soil and the top 15 cm containedsoil contaminated with 1.00% by weight lead. With the packed cylinder ina vertical position 70 cc of the solution as described in Example 1 waspoured on top of the soil. After 24 hours samples taken from the uppercontaminated region, from the mid-point of the cylinder and from thelowest point in the cylinder showed 0.13%, 0.01% and 0.009% by weightlead respectively.

EXAMPLE 8

Four ounces of gelatin were mixed with 70 cc of the solution describedin Example 1. After setting, the viscosity of the solution wassufficient to wet a surface whose contact angle was 86°. This mixturewill wet a vertical surface.

EXAMPLE 9

Three ounces of ordinary household flour were mixed with 70 cc of thesolution described in Example 1. A paste was formed which could easilybe applied to non-horizontal surfaces.

The above examples show how the solution of this invention can be usedto effectively treat lead contaminated surfaces or soil to make themnon-hazardous. The solution is particularly effective on concretesurfaces. When the solution was in contact with a coated concretesurface for a period of 24 hours before the surface was neutralized withwater, the surface of the concrete retained its integrity. Thelead-based surface coating was removed and there was no noticeablepowdering or breakdown of the surface of the concrete.

Good retention of surface properties was also experienced when using thesolution of this invention on wallboard and plaster which had beencoated with a lead-based paint. Since wallboard and plaster are mainlyused on vertical surfaces, the active solution is on the surface for avery short time. In spite of this, the solution was found to be veryeffective in removing the lead-based coating from the wallboard andplaster without affecting the integrity of the wallboard or the plastersurfaces. It was very surprising that the lead-based paint was removedfrom the surface of the wallboard without affecting the felt paper onthe surface of the wallboard and without affecting the structureintegrity of the wallboard. In like manner a plaster surface wasunaffected. This is an extremely important finding since many lead-basedpaint abatement programs specify the removal of wallboard and demolitionof plaster walls because removal is the only suitable means known tothose who formulate the specifications.

It is not desirable to substitute other acids for those specified in theinvention. Hydrofluoric acid is too dangerous a chemical to work with inthe methods of this invention. Also, when hydrofluoric acid was placedin compositions similar to those of the invention, the composition wouldetch window pane in a most undesirable way.

If sulfuric acid were substituted in the compositions of the inventionfor either the nitric acid or the acetic acid, the composition had to beheated to 150° F. for effective removal of lead-based paint from awooden surface.

Use of hydrochloric acid was equally unsatisfactory. Compositionscontaining hydrochloric acid did not affect a lead-based painted woodensurface even after 36 hours of contact.

The above examples show that the composition of the invention performswell in abatement of lead-based coatings regardless of the surface onwhich they are coated and without detriment to the environment of thecoatings.

We claim:
 1. A method for treating lead contaminated surface soilcomprising: (a) applying an aqueous composition comprising about 10 to20 percent by volume of a 30% by weight hydrogen peroxide solution,about 10 to 20 percent by volume ammonium hydroxide, about 10 to 20percent by volume concentrated nitric acid, about 10 to 20 percent byvolume glacial acetic acid to the surface of said soil and (b) allowingsaid composition to migrate through said soil.
 2. The method fortreating the lead-contaminated surface soil according to claim 1 whereinsaid aqueous composition is comprised of about one part by volume of a30% by weight hydrogen peroxide solution, about one part by volumeammonium hydroxide, about one part by volume concentrated nitric acid,about one part by volume glacial acetic acid, and about three parts byvolume water.